The use of powder metal compositions to produce metal products is well-known in the prior art. Powder metals (powder metallurgy) are commonly employed in applications wherein casting, forging or other metal processing techniques is not cost effective. The fabrication of parts using powder metals includes the steps of placing the metal composition in the cavity of a mold, pressing the composition to form a green part, removing the green part from the cavity, and firing the green part.
During the pressing operation, it is generally important that a lubricant be employed in order to facilitate the removal of the green part from the cavity and allow for the slippage of particles against each other so that forces are spread uniformly and density can be made to be as uniform as possible in the cross-section of the pressed part. Generally, in the prior art there are two separate approaches to the use of lubricants. One approach is to apply the lubricant to the wall of the mold cavity prior to adding the metal composition to the cavity, with the metal composition having a relatively low level of lubricant. The downside to this approach is that it is time-consuming to apply a uniform coating of a liquid lubricant to the cavity walls. The second approach is to incorporate a relatively higher level of lubricant into the powder metal composition. However, the use of prior art lubricants results in several adverse effects. Specifically, such lubricants reduce the flow of the powder metal into the mold cavity thereby slowing the pressing operation. Lubricants can also detrimentally impact green density and result in the evolution of undesirable effluents during preheat and the sintering operation. Lubricants can also contribute to low final density in parts, protracted furnace time, and the formation of cracks and blisters during firing.
The present invention provides a lubricant system that overcomes the deficiencies of the prior art lubricant systems.